The present invention relates to a memory device, to methods and apparatus for writing to and reading from the memory, and to associated methods of manufacture. Particularly embodiments of the present invention are suitable for, but not limited to, use as a memory for a computer.
A memory is a device used to store information for subsequent retrieval. The memory may be associated with a computer, or a device including a computational unit e.g. a mobile phone. Information is typically stored in digital form as sequences of bits.
Memory devices can be permanently connected to computational devices, or can be separate devices (e.g. secure digital flash memory) arranged to be removably connected to computational devices. Memory devices are now incorporated within a range of media e.g. many banking cards now incorporate a memory device, for storage of the PIN (personal identification number) of the user, on the card.
There is an ongoing desire within the electronics industry for miniaturisation of electronic/electrical circuits, including memory devices. Known techniques for making integrated circuits of micrometer dimensions commonly involve multiple steps comprising overlying and aligning different shapes and patterns (e.g. photolithographic techniques), with subsequent diffusion and implantation steps. However, miniaturisation of such steps (to manufacture devices of sub-micrometer dimensions e.g. nanometre dimensions) is problematic for a number of reasons, including the precise alignment of the apparatus required between each of the different steps. This leads to a relatively large increase in cost of the fabrication equipment utilised to manufacture such miniaturised devices.
Additionally, as semiconductor device dimensions rapidly reduce to the nanometre scale, physical phenomena arise that can have undesirable effects upon the operation of the miniaturised conventional semiconductor devices. For example, a single-electron transistor (SET) has been found to be extremely sensitive to fluctuating background charges. A single charged impurity in the close vicinity of a SET can seriously influence its operation. Thus, the performance of existing electronic devices can deteriorate, upon miniaturisation, unless a high degree of control of surface physical and chemical properties can be realised.
It is an aim of embodiments of the present invention to address one or more problems of the prior art, whether referred to herein or otherwise. It is an aim of particular embodiments of the present invention to provide a memory device that is relatively simple (and hence cheap) to manufacture.